Jumat, 01 Januari 2010

The sensory exam includes testing for: pain sensation (pin prick), light touch sensation (brush), position sense, stereognosia, graphesthesia, and extinction. Diabetes mellitus, thiamine deficiency and neurotoxin damage (e.g. insecticides) are the most common causes of sensory disturbances. The affected patient usually reports paresthesias (pins and needles sensation) in the hands and feet. Some patients may report dysesthesias (pain) and sensory loss in the affected limbs also. Pain and Light Touch Sensation Initial evaluation of the sensory system is completed with the patient lying supine, eyes closed. Instruct the patient to say "sharp" or "dull" when they feel the respective object. Show the patient each object and allow them to touch the needle and brush prior to beginning to alleviate any fear of being hurt during the examination. With the patient's eyes closed, alternate touching the patient with the needle and the brush at intervals of roughly 5 seconds. Begin rostrally and work towards the feet.

Make certain to instruct the patient to tell the physician if they notice a difference in the strength of sensation on each side of their body.

Alternating between pinprick and light touch, touch the patient in the following 13 places. Touch one body part followed by the corresponding body part on the other side (e.g., the right shoulder then the left shoulder) with the same instrument. This allows the patient to compare the sensations and note asymmetry.The corresponding nerve root for each area tested is indicated in parenthesis.

If there is a sensory loss present, test vibration sensation and temperature sensation with the tuning fork. Also concentrate the sensory exam in the area of deficiency.

Position Sense

Test position sense by having the patient, eyes closed, report if their large toe is "up" or "down" when the examiner manually moves the patient's toe in the respective direction. Repeat on the opposite foot and compare. Make certain to hold the toe on its sides, because holding the top or bottom provides the patient with pressure cues which make this test invalid.

Fine touch, position sense (proprioception) and vibration sense are conducted together in the dorsal column system. Rough touch, temperature and pain sensation are conducted via the spinothalamic tract. Loss of one modality in a conduction system is often associated with the loss of the other modalities conducted by the same tract in the affected area.

Stereognosia

Test stereognosis by asking the patient to close their eyes and identify the object you place in their hand. Place a coin or pen in their hand. Repeat this with the other hand using a different object.Astereognosis refers to the inability to recognize objects placed in the hand. Without a corresponding dorsal column system lesion, these abnormalities suggest a lesion in the sensory cortex of the parietal lobe.

Graphesthesia

Test graphesthesia by asking the patient to close their eyes and identify the number or letter you will write with the back of a pen on their palm. Repeat on the other hand with a different letter or number.Apraxias are problems with executing movements despite intact strength, coordination, position sense and comprehension. This finding is a defect in higher intellectual functioning and is associated with cortical damage.

Extinction

To test extinction, have the patient sit on the edge of the examining table and close their eyes. Touch the patient on the trunk or legs in one place and then tell the patient to open their eyes and point to the location where they noted sensation. Repeat this maneuver a second time, touching the patient in two places on opposite sides of their body, simultaneously. Then ask the patient to point to where they felt sensation. Normally they will point to both areas. If not, extinction is present.With lesions of the sensory cortex in the parietal lobe, the patient may only report feeling one finger touch their body, when in fact they were touched twice on opposite sides of their body, simultaneously. With extinction, the stimulus not felt is on the side opposite of the damaged cortex. The sensation not felt is considered "extinguished".

http://edinfo.med.nyu.edu/courseware/neurosurgery/sensory.html

Tes SensorisSensory testing of the face is discussed in the section on Cranial Nerves. Testing of the extremities focuses on the two main afferent pathways: Spinothalamics and Dorsal Columns.Spinothalamics: These nerves detect pain, temperature and crude touch. They travel from the periphery, enter the spinal cord and then cross to the other side of the cord within one or two vertebral levels of their entry point They then continue up that side to the brain, terminating in the cerebral hemisphere on the opposite side of the body from where they began.Dorsal Columns: These nerves detect position (a.k.a. proprioception), vibratory sensation and light touch. They travel from the periphery, entering the spinal cord and then moving up to the base of the brain on the same side of the cord as where they started. Upon reaching the brain stem they cross to the opposite side, terminating in the cerebral hemisphere on the opposite side of the body from where they began.

A screening evaluation of these pathways can be performed as follows:

SpinothalamicsThe patient's ability to perceive the touch of a sharp object is used to assess the pain pathway of the Spinothalamics. To do this, break a Q-tip or tongue depressor in half, such that you create a sharp, pointy end. Alternatively, you can use a disposable needle as the sharp-ended probe. I would discourage the use of the pointy, metal spikes that accompany some reflex hammers. If, for example, you used this and caused bleeding, it's possible (if the tip were not well cleaned) to transmit blood borne infections from one patient to another. Better to use a disposable implement.Ask the patient to close their eyes so that they are not able to get visual clues.Start at the top of the foot. Orient the patient by informing them that you are going to first touch them with the sharp implement. Then do the same with a non-sharp object (e.g. the soft end of a q-tip). This clarifies for the patient what you are defining as sharp and dull.

Now, touch the lateral aspect of the foot with either the sharp or dull tool, asking them to report their response. Move medially across the top of the foot, noting their response to each touch.If they give accurate responses, do the same on the other foot. The same test can be repeated for the upper extremities (i.e. on the hand), though this would only be of utility if the patient complained of numbness/impaired sensation in that area.

Dorsal Columns

Proprioception: This refers to the body's ability to know where it is in space. As such, it contributes to balance. Similar to the Spinothalamic tracts, disorders which affect this system tend to first occur at the most distal aspects of the body. Thus, proprioception is checked first in the feet and then, if abnormal, more proximally (e.g. the hands).

Technique:Ask the patient to close their eyes so that they do not receive any visual cues.Grasp either side of the great toe. Orient the patient as to up and down. Flex the toe (pull it upwards) while telling the patient what you are doing. Then extend the toe (pull it downwards) while again informing them of which direction you are moving it.Testing Proprioception

Alternately deflect the toe up or down without telling the patient in which direction you are moving it. They should be able to correctly identify the movement and direction.Both great toes should be checked in the same fashion. If normal, no further testing need be done in the screening exam.If the patient is unable to correctly identify the movement/direction, move more proximally (e.g. to the ankle joint) and repeat (e.g. test whether they can determine whether the foot is moved up or down at the ankle).

Similar testing can be done on the fingers. This is usually reserved for those settings when patients have distal findings and/or symptoms in the upper extremities.

Vibratory Sensation: Vibratory sensation travels to the brain via the dorsal columns. Thus, the findings generated from testing this system should corroborate those of proprioception (see above).

Technique:Start at the toes with the patient seated. You will need a 128 hz tuning fork.128 Hz tuning fork Ask the patient to close their eyes so that they do not receive any visual cues.Grasp the tuning fork by the stem and strike the forked ends against the heel of your hand, causing it to vibrate.Place the stem on top of the interphalangeal joint of the great toe. Put a few fingers of your other hand on the bottom-side of this joint.Testing vibratory sensation

Ask the patient if they can feel the vibration. You should be able to feel the same sensation with your fingers on the bottom side of the joint.The patient should be able to determine when the vibration stops, which will correlate with when you are no longer able to feel it transmitted through the joint. It sometimes takes a while before the fork stops vibrating. If you want to move things along, rub the index finger of the hand holding the fork along the tines, rapidly dampening the vibration.

Repeat testing on the other foot.

Additional/Special Testing for Dorsal Column Dysfunction

Testing Two Point Discrimination: Patients should normally be able to distinguish simultaneous touch with 2 objects which are separated by at least 5mm. These stimuli are carried via the Dorsal Columns. While not checked routinely, it is useful test if a discrete peripheral neruropathy is suspected (e.g. injury to the radial nerve).

Technique:Testing can be done with a paperclip, opened such that the ends are 5mm apart.The patient should be able to correctly identify whether you are touching them with one or both ends simultaneously, along the entire distribution of the specific nerve which is being assessed.

Special Testing for Early Diabetic Neuropathy: A careful foot examination should be performed on all patients with symptoms suggestive of sensory neuropathy or at particular risk for this disorder (e.g. anyone with Diabetes). Loss of sensation in this area can be particularly problematic as the feet are a difficult area for the patient to evaluate on their own. Small wounds can become large and infected, unbeknownst to the insensate patient. Sensory testing as described above can detect this type of problem. Disposable monofilaments (known as the Semmes-Weinstein Aethesiometer) are specially designed for a screening evaluation. These small nylon fibers are designed such that the normal patient should be able to feel the ends when they are gently pressed against the soles of their feet.Monofiliment

Technique: Have the patient close their eyes so that they do not receive any visual cues.Touch the monofilament to 5-7 areas on the bottom of the patient's foot. Pick locations so that all of the major areas of the sole are assessed. Avoid calluses, which are relatively insensate.The patient should be able to detect the filament when the tip is lightly applied to the skin.Monofiliment testing: Patients with normal sensation should be able to detect the monofiliment when it is lightly applied (picture on left). If the force required to provoke a sensory response is strong enough to bend the monofiliment (picture on right), then sensation is impaired.

Interpretation: If the examiner has to supply enough pressure such that the filament bends prior to the patient being able to detect it, they likely suffer from sensory neuropathy. Testing should be done in multiple spots to verify the results. Patient's with distal sensory neuropathy should carefully examine their feet and wear good fitting shoes to assure that skin breakdown and infections don't develop. Efforts should also be made to closely control their diabetes so that the neuropathy does not progress.Neuropathic Ulcer: Large ulcer has developed in this patient with severe diabetic neuropathy.

Interpreting Results of Sensory Testing

Patterns of Impairment for the Spinothalamic Tracts:Patients should be able to correctly distinguish sharp sensation, indicating normal function of the spinothalamic pathway.Mapping out regions of impaired sensation: The examination described above is a screening evaluation for evidence of sensory loss. This is perfectly adequate in most clinical settings. Occasionally, the history or screening examination will suggest a discrete anatomic region that has sensory impairment. When this occurs, it is important to try and map out the territory involved, using careful pin testing to define the medial/lateral and proximal/distal boundaries of the affected region. You may even make pen marks on the skin to clearly identify where the changes occur. As most clinicians have not memorized the distributions of all peripheral nerves or spinal nerve roots, you can simultaneously consult a reference book to see if the mapped territory matches a specific nerve distribution. This type of mapping is somewhat tedious and should only be done in appropriate situations.Diffuse Distal Sensory Loss: A number of chronic systemic diseases affect nerve function. The most commonly occurring of these, at least in Western countries, is Diabetes. When control has been poor over many years, the sensory nerves become dysfunctional. This first affects the most distal aspects of the nerves and then moves proximally. Thus, the feet are the first area to be affected. As it is a systemic disease, it occurs simultaneously in both limbs. Exam reveals loss of ability to detect the sharp stimulus across the entire foot. Thus, the sensory loss does not follow a dermatomal (i.e. spinal nerve root) or peripheral nerve distribution. As the examiner tests more proximally, he/she will ultimately reach a point where sensation is again normal. The more advanced the disease, the higher up the leg this will occur. Hands can be affected, though much less commonly then feet as the nerves traveling to the legs are longer and thus at much greater risk. This pattern of loss is referred to as a Stocking or Glove distribution impairment, as the area involved covers an entire distal region, much as a sock or glove would cover a foot or hand. Such deficits may be associated with neuropathic pain, a continuous burning sensation affecting the distal extremity.Peripheral Nerve Distribution: A specific peripheral nerve can become dysfunctional. This might, for example, occur as the result of trauma or infarction (another complication of diabetes). In this setting, there will be a pattern of sensory impairment that follows the distribution of the nerve. Radial nerve palsy, for example, can occur if an intoxicated person falls asleep in a position that puts pressure on the nerve as it travels around the Humerus (bone of the upper arm). Intoxication induced loss of consciousness then prevents the patient from reflexively changing position, the normal means by which we prevent nerves from being exposed to constant direct pressure. The resultant sensory loss would involve the back of the hand and forearm. Motor function would also be affected (see under motor exam). Pinning down the culprit nerve requires knowledge of nerve anatomy and innervation. On a practical level, most clinicians don't commit this to memory. Rather, they gather a history suggestive of a discrete nerve deficit, verify the territory of loss on exam, and then look it up in a reference book.

Nerve Root Impairment: A nerve root (or roots) can be damaged as it leaves the cord. This will result in a sensory deficit along its specific distribution, which can in turn be identified on examination. The S1 nerve root, for example, can be compressed by herniated disc material in the lumbar spine. This would cause sensory loss along the lateral aspect of the lower leg and the bottom of the foot. Only the leg on the affected side would have this deficit. As mentioned under peripheral nerve dysfunction, most clinicians do not memorize the dermatomes related to each nerve root. Rather, they gather a history suggestive of a discrete nerve deficit, verify a dermatomal distribution of loss on exam, and then look it up in a reference book.

The Spinothalamics are also responsible for temperature discrimination. For practical reasons (i.e. it's often hard to find test tubes, fill them with the requisite temperature water, etc) this is omitted in the screening exam. The information from sharp stimulus testing as described above should suffice. Temperature discrimination could be assessed as a means of verifying any abnormality detected on sharp/dull testing.Testing of the sacral nerve roots, serving the anus and rectum, is important if patients complain of incontinence, inability to defecate/urinate, or there is otherwise reason to suspect that these roots may be compromised. In the setting of Cauda Equina syndrome, for example, multiple sacral and lumbar roots become compressed bilaterally (e.g. by posteriorly herniated disc material or a tumor). When this occurs, the patient is unable to urinate, as the lower motor neurons carried in these sacral nerve roots no longer function. Thus there is no way to send an impulse to the bladder instructing it to contract. Nor will they be aware that there bladders are full. There will also be loss of anal spincter tone, which can be appreciated on rectal exam. Ability to detect pin pricks in the perineal area (a.k.a. saddle distribution) is also diminished.

Patterns of Impairment for Dorsal Column Dysfunction:

Proprioception:

Patients should be able to correctly identify the motion and direction of the toe. In the setting of Dorsal Column dysfunction (a common complication of diabetes, for example), distal testing will be abnormal. This is similar to the pattern of injury which affects the Spinothalamic tracts described above.

Vibratory Sensation:Patients should be able to detect the initial vibration and accurately determine when it has stopped. As described under testing of proprioception, dorsal column dysfunction tends to first affect the most distal aspects of the system. When this occurs, the patient is either unable to detect the vibration or they perceive that the sensation extinguishes too early (i.e. they stop feeling it even though you can still appreciate the sensation with your fingers on the underside of the joint).The findings on vibratory testing should parallel those obtained when assessing proprioception, as both sensations travel via the same pathway.

DISCLAIMER

The content of this Website is not influenced by sponsors. The site is designed primarily for use by qualified physicians and other medical professionals. The information contained herein should NOT be used as a substitute for the advice of an appropriately qualified and licensed physician or other health care provider. The information provided here is for educational and informational purposes only. In no way should it be considered as offering medical advice. Please check with a physician if you suspect you are ill.